This invention relates to a drill bit and sub-assembly for use with a reverse circulation hammer type drill pipe.
Conventional reverse circulation hammer drill bits have generally been unable to provide a high consistency of recovery of core samples throughout the depth of the drilling operation. Lack of consistent air flow and pressure through the central return has caused inconsistent recovery of samples which has resulted, in many cases, in incorrect and misleading mineral content assays of the sample. Additionally, the design of conventional hammer drill bits has resulted, not only in lack of consistency of recovery of core samples, but also in inefficiency in drilling.
The primary object of the present invention is to improve consistency of recovery of core samples and efficiency of drilling. The primary object is achieved by improvements in the construction and design of the drill bit and sub-assembly which improve cutting and removal of chips and maintenance of air pressure in the inner pipe.